In some applications, a banknote stacker must successfully stack banknotes with widely varying characteristics. For example, when used in conjunction with a banknote validator in a vending machine placed in a health club, the stacker may be faced with stacking banknotes ranging from crisp, new, dry banknotes to worn, torn, wet banknotes. Many other extreme examples might be listed, but it suffices to say that a currency stacker preferably should be able to properly stack without jamming widely varying currency under widely varying conditions.
In certain prior art stackers, after validation, a banknote falls by gravity into a compartment which is much wider than the banknote, and then a pusher plate pushes the banknote into a banknote magazine. Understandably, this simple arrangement will achieve poor stacking results if a worn, old banknote falls into the compartment and collapses under its own weight before the pusher plate operates.
Other prior art stackers maintain positive control of a banknote while driving it to a position proximate a pusher plate using pulleys, drive belts, and pinch rollers. In such arrangements, the banknotes are gripped or frictionally held between the driving components located on either side of the banknote. For example, pinch rollers may be mounted on leaf springs to insure that the banknote is adequately pinched or gripped by the pinch rollers. Problems with this kind of arrangement can arise because no matter how carefully such systems are designed, as the pusher attempts to push the banknote into the banknote magazine, the two gripped sides of the banknote will not pull free at exactly the same time. Both improper stacking and jamming can result. For example, if one side of the banknote pulls free and the other does not, the banknote tends to wrap around into a C-shape, and either is not properly stacked or causes a jam when the stacker receives another banknote.